Does MusicMatch Jukebox allow you to record cassette tapes to MP3? I thought it did, but haven't used it in a while. If it can, you could just plug in an external CD player to the audio in jack and record the music to a MP3 file. You would then need to manually enter the artist, song title and other data manually. There are other programs that allow you to do this as well. Unfortunately I only that you can do this, and don't have first hand experience.
Downloading them from somewhere would probably be easier though.
goates